A pneumatically-powered device suitable for stunning fish is described in International Application No. PCT/AU2005/000412 (Publication No. WO 2005/091558) by the present applicant. This device can be efficiently used for the stunning of large numbers of fish in an automatic, flow-through fashion and is incorporated herein by cross reference.
The operating principle of the stunning device according to the invention described in WO 05/091558 involves the killing of the fish by a blow to the head that is administered by the piston of the gun. Activation of the piston results from the head of the fish contacting the trigger. The trigger and piston are configured such that when the piston is activated, it strikes the fish just behind and/or between the eyes. This impact is sufficient to kill the fish due to the shock to the brain. After the fish has been killed by the force of the piston, the gun assembly, the trigger which typically comprises a contact plate, and vertical guide plates pivot from the set point to a retracted position, wherein the retracted position is sufficient to allow the stunned fish to pass beyond the set point. On passage of the fish out of the channel of the device, the fish activates a sensor that in turn activates the pivot mechanisms and returns the gun assembly, trigger and vertical guide plates to the set point, thereby effectively resetting the device.
This device is extremely efficient at stunning large numbers of fish and has achieved considerable commercial success. In some circumstances, however, the device performs an unwanted operation which is known in the trade as “hammering”. “Hammering” occurs when a processed fish has not completely exited from the device before the gun assembly, trigger and vertical guide plates move from the retracted position to the set point. When this happens the trigger contacts the processed fish in the course of its downward trajectory, resulting in the activation of the gun and pivot mechanisms before the gun has reached the set point. As a consequence the processed fish suffers multiple piston strikes, resulting in damage to the vendible portions of the fish. Elimination of this unwanted operation would therefore be an advantage.
Fish, such as salmon, require labour intensive preparation before sale. Typically fish are caught, stunned, bled and immediately placed in cold storage. Bleeding is an essential step in this process as it improves the appearance of the meat and enhances its flavour. Devices described in WO 2005/091558 are commonly employed on fish processing lines upstream of the bleeding step which is performed manually. Manual bleeding is a labour intensive process and is therefore a rate limiting step in the overall processing of the fish. A fortiori because of the speed with which fish are stunned by the device there is a considerable lag between stunning and bleeding which may affect the quality and therefore sale price of the meat. It will also be appreciated that before slaughter, fish in aqua-farms are typically tagged and/or inoculated. These tasks are also labour intensive and costly due to the number of man hours required to carry them out. Therefore, a device that comprises one or more fish processing means—for example a pneumatic gun and a pneumatic blade; a means for inoculating fish; or a means for tagging fish—and which can process large numbers of fish in an automatic, flow-through fashion would offer a considerable advantage to an operator of a commercial fishery.
It is an aim of the invention to provide a device, that operates in a similar manner to the device described in WO 05/091558, yet is significantly enhanced in that the device comprises: one or more fish processing means that can be used in an automated flow-through manner; and a mechanism that resets the device whilst avoiding the premature activation of the at least one fish processing means.